Are Lawn Mower Engines Interchangeable? (Solved)

Lawn mowers lined up at retailer

Once an engine deteriorates on a lawn mower, it makes cutting your lawn much more difficult.

There are a few things you can do to prolong the life of a mower, but eventually, it will reach the point of no return.

And is buying a new mower always necessary? Or are lawn mower engines interchangeable?

It certainly would be a lot cheaper to put a new engine in than buy a new mower, but is it feasible?

We take a closer look at that in this article.

So let’s get started…

Are Lawn Mower Engines Interchangeable?

Lawn mower engines are generally interchangeable, and with a little research, you should have no problem finding a new engine to fit in your mower if your old engine has blown. To make it as easy to mount as possible look for a new engine with the same shaft size and bolt pattern and one that will fit into the space available.

Changing A Lawn Mower Engine – What You Need to Consider

The good news is, for the most part, you can swap pretty much any engine, although some swaps will be harder than others.

To help I have included a couple of videos walking you through the procedure in this post.

Push mower engines tend to have standard mounting points which means they can be swapped relatively easily between the chassis of any gas push mower.

On riding mower engines the bolt pattern is generally standardized, especially on vertical driveshafts, so they too are interchangeable.

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That said there might still be a few issues you could run into…

Shaft Size

First things first, check the length and diameter of the crankshaft on both engines, if they are the same then you have nothing to worry about.

If they are different then you will need to get a replacement pulley set of the same shaft and pulley diameters and fit that.

The easiest option is to get an engine with the same shaft size and length.

There are engine suppliers such as Small Engine Warehouse and OPE Engines that can help. Just give them the spec number of your current engine or the serial and model number of your mower.

Engine Style

Make sure you get the right style of engine as well. Is it a horizontal or vertical driveshaft? Most riding mowers are vertical shaft engines for instance.

What type of engine is it?

Most OHV engines swap pretty seamlessly, but is it a single or a twin? 

An opposed twin engine might be too wide to fit where a single or V-Twin engine was. Which can lead to another problem in itself…

Engine Size

If you are going to buy a new engine, make sure the hood space will accommodate it.

On your mower measure the underside of the width and depth of the hood.

On a potential new engine measure from the bolt flanges to the top of the motor and side to side.

As long as it fits, it should swap in fairly easily as most riding mowers have pre-drilled bolt patterns designed to accommodate different types of engine.

But obviously, you want the hood of your mower to be able to close and if the new engine is too big, then there is no way to rectify that!

Bolt Pattern

We have touched on this already, but the bolt patterns on most vertical driveshaft engines, and most engines used in push mowers, are very similar regardless of make.

That allows mower manufacturers to specify more than one engine for a particular line of their mowers.

But there will always be exceptions to this rule!

If the mounting holes don’t match up, you can always drill new holes just make sure the shaft sits as close as possible to the same location of the original motor.

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Mufflers can be a problem as they are often part of the mower rather than the engine.

Also, they come in a variety of styles, such as screw-in mufflers and mufflers that fit under the frame.

You can always buy and install a new muffler and or even improvise with the current muffler to find a solution.

Horse Power

You shouldn’t worry too much about the difference in horsepower between a new engine and an old engine.

Belts connect the engine to the hydros and to the pulleys, but they turn the same RPMs regardless of whether it is a 14hp engine or a 20hp engine so it won’t hurt your mower.

It is a very different setup from a car for instance which does have parts that take power directly from the engine.

Wiring Harness

Check the wiring harness on both the old and the new engine.

If the wiring is different it is usually just a case of making a note of what each wire does on the old engine and finding the corresponding connection on the new one.


You will need to check the throttle and choke cables as they might not be compatible with the new engine.

Usually the worst-case scenario here is you just need longer or shorter cables. Check also if the choke is part of the throttle or a separate cable.

Replacement cables are reasonably cheap and mounting them is very straightforward.

Gas Line

It is a similar case with the gas line which may need to be lengthened or shortened.

Also if you are replacing the engine on a riding mower you will find some are gravity-fed and others are pumped.

If your mower is pumped you will want to find an engine with an impulse port that you can hook a pump up to.

If it is gravity fed you don’t need to worry about this.

Manual Deck Engagement of Electric PTO?

If your mower has an electric clutch for PTO and the new engine does not, it might not generate enough charge to run the electric PTO. Bear this in mind.

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Final Thoughts

Are Lawn Mower Engines Interchangeable infographic

If you are considering swapping the engine of your mower for another one it can be quite an intimidating thought, but remember, as I said, you can swap almost any engine.

And whilst there are a few problems you might encounter (outlined in our infographic above) , with a bit of planning they can all be overcome.

A good starting point is to get an engine with the same mounting holes and that is the same shaft size and type as your old engine.

Measure everything up and make sure it will fit under the hood.

And they really are the main things to consider, if all of those factors line up you can interchange the engines fairly easily.

Many engine suppliers such as Small Engine Warehouse and OPE Engines will be only too happy to help as well.

You really should not have a problem finding a new engine that can be easily interchanged.

Good luck!

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1 thought on “Are Lawn Mower Engines Interchangeable? (Solved)”

  1. I have muffler on right side on my old B&S but new engines have mufflers on left side my left side is on drivers side I need muffler on front off mower or left side off mower looking from front
    Left side of mower is front of engine


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